Jerusalem–Israelis want to rejoice over the outbreak of protests in Egyptâ€™s city squares. They want to believe that this is the Arab worldâ€™s 1989 moment. Perhaps, they say, the poisonous reflex of blaming the Jewish state for the Middle Eastâ€™s ills will be replaced by an honest self-assessment.

But few Israelis really believe in that hopeful outcome. Instead, the grim assumption is that it is just a matter of time before the only real opposition group in Egypt, the Islamist Muslim Brotherhood, takes power. Israelis fear that Egypt will go the way of Iran or Turkey, with Islamists gaining control through violence or gradual co-optation.

Either result would be the end of Israelâ€™s most important relationship in the Arab world. The Muslim Brotherhood has long stated its opposition to peace with Israel and has pledged to revoke the 1979 Egyptian-Israeli peace treaty if it comes into power. Given the strengthening of Hezbollah in Lebanon, Hamasâ€™s control of Gaza and the unraveling of the Turkish-Israeli alliance, an Islamist Egypt could produce the ultimate Israeli nightmare: living in a country surrounded by Iranâ€™s allies or proxies.

Mohamed ElBaradei, the icon of the Egyptian protesters, and many Western analysts say that the Egyptian branch of the Brotherhood has forsworn violence in favor of soup kitchens and medical clinics. Even if that is true, it is small comfort to Israelis, who fear that the Brotherhoodâ€™s nonviolence has been a tactical maneuver and know that its worldview is rooted in crude anti-Semitism.

The Brotherhood and its offshoots have been the main purveyors of the Muslim worldâ€™s widespread conspiracy theories about the Jews, from blaming the Israeli intelligence service for 9/11 to accusing Zionists of inventing the Holocaust to blackmail the West.

The fear of an Islamist encirclement has reminded Israelis of their predicament in the Middle East. In its relationship with the Palestinians, Israel is Goliath. But in its relationship with the Arab and Muslim worlds, Israel remains David.

Since its founding, Israel has tried to break through the military and diplomatic siege imposed by its neighbors. In the absence of acceptance from the Arab world, it found allies on the periphery of the Middle East, Iran and Turkey. Peace with Israelâ€™s immediate neighbors would wait.

That doctrine began to be reversed in 1979, when the Israeli-Iranian alliance collapsed and was in effect replaced by the Egyptian-Israeli treaty that same year. The removal of Egypt from the anti-Israeli front left the Arab world without a credible military option; indeed, the last conventional war fought by Arab nations against Israel was the 1973 joint Egyptian-Syrian attack on Yom Kippur.

Since then all of Israelâ€™s military conflicts â€” from the first Lebanon war in 1982 to the Gaza war of 2009 â€” have been asymmetrical confrontations against terrorists. While those conflicts have presented Israel with strategic, diplomatic and moral problems, it no longer faced an existential threat from the Arab world.

For Israel, then, peace with Egypt has been not only strategically but also psychologically essential. Israelis understand that the end of their conflict with the Arab world depends in large part on the durability of the peace with Egypt â€” for all its limitations, it is the only successful model of a land-for-peace agreement.

Above all, though, Israeli optimism has been sustained by the memory of the improbable partnership between President Anwar el-Sadat of Egypt and Israelâ€™s prime minister, Menachem Begin. Only four years before flying to Tel Aviv on his peace mission, Sadat had attacked Israel on its holiest day. Begin, Israelâ€™s most hawkish prime minister until that time, withdrew from the Sinai Peninsula, an area more than three times the size of Israel.

Though Egypt failed to deliver the normalization in relations Israelis craved, the thousands of Israeli tourists who have filled the beaches of the Sinai coast experienced something of the promise of real peace.

At least in one corner of the Arab Middle East, they felt welcomed. A demilitarized Sinai proved that Israel could forfeit strategic depth and still feel reasonably secure.

The Sinai boundary is the only one of Israelâ€™s borders that hasnâ€™t been fenced off. Israelis now worry that this fragile opening to the Arab world is about to close.

Yossi Klein Halevi is a fellow at the Shalom Hartman Institute and a contributing editor to The New Republic.